Distillation of organic liquids



Sept. 29, 1942. A. P. LEE

DISTILLATION OF ORGANIC LIQIDS Filed Deo. 1, 1938 2 sheets-sheet 1INVENTOR t L ATTORNEY Sept. 29; 1942. A. P. LEE

DIS-TILLATION OF ORGANIC LIQUIDS Filed Deo. l, 1938 2 ShetS-Sheet 2 AllINVENTOR;

22a ATTORNEY.

Patented Sept. 29, 1942 .UNITED STATES PATENT OFFICE 2,297,004 j vDis'rrLLA'rIoNoF ORGANIC LIQUms Alan Porter Lee, Madison, N. J.

Application December 1, 1938, Serial No.' 243,307

s claims. (01.202-46) This invention relates to improvements in methodsof distilling organic liquids in column stills and particularly toimprovements in the procedure of returning undistilled residues to the,distilling zone, known as recycling, in the distillation of organicliquids. Examples of such liquids are fatty acids-the products ofhydrollysis of` tallows, greases, fatty oils, soapstocks and similarproducts; fatty oil stocks containing fatty acids which are to beseparated by distillation; petroleum derivatives or fractions of variousboiling points, particularly lubricant stocks, residuesfrom crackingstills, fuel oil stocks, asphalts and Y other high-boiling fractionsofpetroleum oils;v glycerine; benzenevand liquid derivatives thereof;organic esters; tars; waxes and the like.

It is an. object of this invention to provide, for use in connectionwith the distillation of such products, a method of recycling residueswhich will facilitate increased efliclency of separation of thedistillates from the residues.

Another object of the invention is to provide an economical method ofreheatlng the recycled residues in order to promote additional recoveryof distilled product from said residues.

Another object. of'my invention is to'provide an economical method ofsupplyingheat to the intermediate and upper portions of the distillingcolumn..

A further object .of my invention is to provide means and a method ofcontinuous selective separation of distillation residues.. returning tothe distilling column a portion of the residue containing economicallyrecoverable distillable material, whiledischarging away from thedistilling column another portion of the residue from which sucheconomically distillable material has been recovered.

This application isa continuation in part of my United States LettersPatent 2,177,664, issued October 3l, 1939.

The above-mentioned objects and other objects of this invention will befully understood from the accompanying drawings, which diagrammaticallyshow preferred embodiments of my invention. It is to be understood thatthe example' herein described. is by way of illustration only and not oflimitation and that it may be applied to all other embodiments withinthe scope of this invention, as will be hereinafter fully disclosed.

The example given describes the operation of my invention in conjunctionwith the process of `vacuum distillation of mixed fatty acids, but it isto be understood that my invention is applicable to recyclingdistillation residues in the distillation of other organic liquids andis not limited to the recycling of residues in fatty acid distillation.

It is well known that almost any dis'tilling column can be reduced in4overall height and thei number of trays reduced (in tray-containingcolumns) by recycling a portion of the distillation residues from thebottom to an intermediate portion of the column (below the'feed inlet)for redistillation and the recovery of additional distillable materialfrom such recycled residues.

One ordinary method of recycling the residues involves use of amechanically operated force pump to withdraw the residues from thebottom of the'column and force them to the desired A point of re-entryto the column.

.and similarl heavy, viscous materials, the resi-y dues are ofsuchjheavy or tarrynature, even at the elevated temperature of thestill, that recirculation by ordinary means becomes diilicult and oftenimpossible. In addition, such residues tend to cool rapidly, becoming oncooling'very much more viscous.

In my invention I utilize a steam-lift pump operated by superheatedsteam at a temperature considerably above that of thedistillation-residuesto withdraw such residues from a lower portion ofthe distillation Vcolumn and return them to an intermediate portion ofsaid column for further distillation of recoverable distillate from saidresidues.

In passing through the steam-lift pump, the recirculating residues areintimately admixed with the superheated steam which is used as theactuating force of the pump and said residues ar Ythereby reheated forpromotion of vfurther distillation from them. A, Y

This superheated'steam enters the distilling Y column with the recycledresidues and becomes useful inthe intermediateand upper portions ofAthe-distilling column in promoting vaporization of distillable materialand insupplying heat which is useful in distillation in replacing heatlost by radiation from the said intermediate and upper portions of thecolumn.

My invention provides means and a method of selecting for continuousreturn to the distilling column for redistillation that portion of thedistillation residues which contains a large proportion of distillablesubstances, while continuously withdrawing from the distillation zonethat remaining portion of said residues which contains a lowerproportion of such distillable substances.

This is accomplishedy as will be explained fully herein, by suitablearrangement of the suction connection for withdrawal from the distillingcolumn of redistillable residues by the recirculating steam-lift pump,in relation to a controlled outflow arrangement adapted to withdrawalfrom the distilling column and complete discharge outside the system ofthat portion of the residues which is not economically redistillable.

The accompanying drawings are presented in illustration of equipmentassemblies suitable for use in application of my invention to recyclingthe l of one form of the assembly of a distilling column with steam-liftpump residue reheater and recir- 'culator, with equipment for continuouscontrolled removal of a portion of the residues and with steamsuperheater.

Referring to Figurev 1, which is an elevation, partly in section, ofsuitable apparatus for operation of my invention, pipe line I is thecharging line through which the mixture of fatty acids orfatty-acid-containing stock is fed to the apparatus by gravity or byother suitable means. In the usual operation of commercial fatty aciddistillation the stock fed may contain from 90% to 98% of mixed fattyacids, th'e remainder consisting of neutral fat, unsaponiflable materialand traces of moisture. The material fed into the system throughcharging line l may be at any suitableI temperature for its pipe lineow, varying from room temperature for liquid fatty acids to 150- 175 F.for higher melting mixtures. The stock to be distilled is fed thusthrough pipeline I into and through the shell-and-tube 'neat exchanger2, where it is heated by means of any suitable hot fluid, preferablysteam, to any convenient temperature of initial heat or preheat, such as225 to 300 F., and preferably not over 275 F., for avoidance of localoverheating and consequent decomposition. The temperature of th heatingfluid may be from 300 to 375 F. or lower, but not substantially higher,

From the preheater 2 the stock to be distilled v passes through thepipeline 3 tothe atomizer 4,

where it is thoroughly mixed, atomized and sprayed with from five tofifty or more times its 'own volume of steam. The effect of this atom-4ization is to break up the solid stream of flowing the interiorsurfaces of the tubes 5, 5 in the heater 5, through which the mixturenext passes is thus avoided. In this manner any local overheating,

f decomposition, charring, or carbonization, is prevented. Theatomization with steam also increases the velocity of flow and theturbulence of the atomized mist, thus contributing further to theavoidance of film formation in the tubes of the heater.

The atomization of the stock with steam may be accomplished by anysuitable means, such as a steam ejector, revolving vanes, spray nozzles,

mixing valve, burner-type atomizer or any suitable combination of suchmeans. In the process herein described the atomizing means consists of asteam-ejector-type mixing valve as shown at 4 in Figure 1. The volume ofsteam being many times that of stock, the resultant mixture consists ofmany particles of stock surrounded by an ,atmosphere of steam. Othersuitable means of atomization' may Ibe substituted for that shown.

For the steam used for atomization, any inert gas, such as nitrogen,might be substituted, in which c'ase the atomizing gas would preferablybe preheated to a temperature equal to or slightly higher than that ofthe stock to be atomized. When steam is used it may be saturated orslightly superheated steam.

The atomized mixture of stock and steam passes through the heating tubes5, 5 of the mist heater coil, being heated therein by direct contact onthe outer walls of the tubes .of the gases of combustion of suitablefuel, as for example, natural gas, fuel oil or coal. In one applicationof my invention, Waste gases which have previously been utilized forsuperheating steamv are employed to heat the mixture of steam and fattyacids passing through the tubes 5, 5, means being provided to controlthe temperature of the gases when contacting the tubes 5, 5, raisingthis temperature by admission through bypass I0 (shown in closedposition) of some gases not previously utilized and lowering it byadmission of air through the tempering damper or dampers, II and IIa.Suitable temperature'of Ygases entering the stock-steam heater pass 9ahave been found to be between 650 and 950 F., preferably 850 F.

The atomized mixture of steam and stock is heated very rapidly whilepassing through the tubes 5, 5 of the pass 9a, a convenient rate beingabout 800 F. per minute, the heating being carried to a point below thevaporization temperature of the stock under the pressure conditions ofthe heater, but considerably above the vapori- Zation temperature of thesame stock under the subatmospheric pressure conditions which it nextencounters in the distillation or flashing chamber I2. Suitable maximumtemperatures for the atomized stock and steam mixture when distillingfatty acids are from 400 to 600 F. and preferably 475 to 525o F.,although depending in some measure upon the composition of the stock andthe labsolute pressure conditions in the distilling apparatus. Afterbeing heated in the tubes 5, 5, where the pressure is maintained at anaverage of 8 lbs. per square inch gauge or less, the mixture of stockand steam passes through the pipe 6 and the control valve 8 into thedistillation chamber I2, which is maintained under relatively lowsubatmospheric pressure, from 1" to 10 mercury absolute, and preferablyabout l `at between 575 and 650 F., when using steam dependingupon theamount of distillation steam employed. 'I'he distillation chamber maytake any well-known form, as, for example, a plain cylinder, a towerpacked with material for increasing evaporative surface,l ascreen-baille tower or a bubble-cap tray tower. In this instance thechamber is shown as a bubble-cap plate tower I2, having several platesI3,v I3, each plate being equipped with a plurality of bubblecaps Il, I4and vapor chimneys I5, I5. Each plate is equipped also with an overflowpipe I6.

When 'the atomized mixture of steam and stock enters the vacuum chamberI2 through the valve 8, the steam expands, and the stuck, being aboveits volatilization temperature for the pressure conditions of the vacuumchamber, commences to volatilize rapidly. Both these conditions causeconsiderable `drop in temperature in they stock, which drop amounts-inpractice to 40 to 90 F.

AIn the instance shown the stock and steam mixture is introduced justabove the lowest upper tray I3c of the bubble tower. The steam and theimmediately vaporized fatty acids rise in the tower toward the next trayabove, while that part of thestock which remains unvaporized falls to-Ward the tray I3c. 'I'he mixed vapors pass at temperatures between 800and 900 F. before expansion into the tower.

When the pool of unvaporized stock on the tray I3c below the stock-steaminlet pipe becomes of depth just greater than the projection above thetray of the `top of the overflow pipe ISe, the surplus stock overows tothe next lower tray I3d, where it forms a new pool of material lower infatty acid content than the original stock. In similar manner pools areformed on each succeeding tray below the point where the atomizedstock-steam mixture enters the tower. As the superheated steam enteringthe bottom of the tower expands, rises through the bubble-` cap chimneysand is distributed by the bubble-v caps through the pool of material onthe lowest tray, the bulk of the fatty acids remaining in this materialwill be vaporized, with the aid of the partial pressure of thesuperheated steam. The

mixed steam and distillate vapors will rise through the chimneys andcaps in the next upper tray I3b and much of the vaporized fatty acids iscondensed, forming on the tray a pool of fatty acids of considerablypurer quality than the original stock.' The depth of this pool iscontrolled by the overilow pipe I6b, which carries to the next lowertray all condensation in excess of the amount necessary to maintain ashallow pool on the upper tray I 3b. The unvaporized stock likewiseforms a pool on the first tray I3c below the feed inlet.

Steam at boiler pressure, in this case 145 lbs. per square inch(temperature 363 F.) is taken from the steam. header 1 through the pipeI1 and superheated in the pipe coil I3 in furnace 9 to vinal temperatureofv 900v to A1000 F. In passing through the pressure reducing andregulating valve I9, its pressure is reduced to 3-10 lbs. per

square inch gauge and its temperature falls to '750-900 F., normally 850F. Any suitable fuel is burned at the burner 35 in furnace 9, the gasesof combustion passing over the steam sui'ierhe'at-` ing coil I8 in space36, .then through pass 9a over the heating tubes 5, 5A through whichlatter tubes is passed the atomized stock-steam mixture which is to`bedistilled, the gases passing finally out through the breeching 38 andthe stack 39.

Control of temperature of the gases passing over the tubes 5,- 5-issecured by means of the hot-gas bypass damper I0 and the temperingdampers II and IIa.

The reduced-pressure superheated steam is conducted through pipe 20,control valve 2| and nozzle 22 to the center of the tower I2 at a pointjust below the bottom. bubble-cap plate I3f. This superheated steamserves two purposes, first, to aid distillation of the fatty acids andsecond, to supply heat to replace that consumed in evaporation of thestock`and in radiation from the apparatus.

As the steam expands through the control valve 2| out of the supply pipezone of pressure of 3 to 10 lbs. per square inch gauge, into the bottomarea of the tower at pressure of 21/2 to 3" of mercury absolute, thereis marked coolinr of the steam due 'to expansion, which enablesregulation of thetemperature of this bottom area descending unvaporizedstock becoming progres` sively poorer in vaporizable material as itappreaches the bottom tray.` Y

.The rising mixed vapors of superheated stea and distillate becomeprogressively cooler as they pass upward through the tower, from theell'ects of expansion, evaporation A and radiation. f The descendingstream of liquid material likewise tends to become progressively coolerin descending through the' tower, from the eiects of evaporation andradtion. As the operation progresses, this tendency of the descendingstock to become cooler is overcome, in part by the heating eiiect ofpartial condensation of distillate vapors in the pool of liquid on eachtray and partly by the heat supplied by the superheated steam, so thatwhen the operation reaches the desired state of continuous equilibrium,the descending liquid stockincreases in temperature on each succeedinglower tray, while the ascending vapors decrease in temperature as theyrise through the tower. The liquid residue owing awayfroml the bottomtray I3f, in fatty acid distillation is at a temperature of 505 to 595F. and preferably 580 F. when distilling standard mixed fatty acidsfrom. tallow grease. It is to be noted that for best results, thistemperature of material leaving thebottom tray may suitably be variedover a' wide range, depending upon the type of material treated. Forcertain fatty acids of vegetable origin, this bottom tray temperaturesuitably may be carried as low as 400 F., or even lower.

The residue flows from the bottom plate through the overflow pipe I6finto the cup seal 23, out of which it falls .toa sump at the bottom ofthe tower, forming there a pool, the depth of which is controlled by theinverted syphon pipeloop 24. 1

In my invention I utilize a steam-liftpump operated by superheated steamat a temperature considerably above that of the residues to drawdischarge pipe 21 and the valve 28 into the distillation chamber at apoint above the third tray from bottom,-l3d, or alternatively to thenext lower tray I3e through the valve 28a, or through both these valves.to both the trays simultaneously. Superheated steam at 3 to 10 lbs.pressure and temperature of about 850 F. is takenfrom the pipe-line 20through the valve 29 and the pipe 30 for operation of the steam-liftpump 26.

The use of the steam-lift pump operated by superheated steam has severaladvantages. The temperature of the residues is raised, thus aidingfurther distillation of vaporizable material from these residues. Thesuperheated steam used for the steam-lift pump mixes with the residuesand its vapor pressure is utilizable in the distillation from the traysabove the point of its entrance into the tower. The addition of theextra heat units of this superheated steam is useful in economicalreplacement of heat lost by radiation from the central and upperportions of the tower and in maintenance of vaporizing temperatures onthe upper plates.

Despite the admixture of steam with the residues and the injection' ofthis mixture into the median portion of the distilling zone, in myprocess no entrainment of coloring matter from the residues is apparentin the distilled fatty acid vapors leaving the upper exit of the tower.l

By variation of the volume of superheated steam fed to the steam-liftpump, the quality and amount of nal residue can be controlled, theamount recirculated controlling the net amount of final residue outflow.As the amount of material recirculated is increased, the amount ofdistillation steamadded to the tower through the supply pipe nozzle 22likewise must be increased, to provide for the increasing distillationburden on the lower trays. The amount of steam utilized by the recyclingsteam-lift pump, however, is also used as distillation steam and doesnot increase the total steam input whichwould be required to obtaincomparable distillation results in similar apparatus without thisfeature.

'I'he heavier residues, sinking to the lowest point of the pool formedin the sump 31 at the tower bottom and comprising all surplus which isnot recycled by the steam-lift pump 26, flow through the pipe 3| andinverted syphon 24 into the pitch receiver 32, which is connected to thetower I2 by the vacuum-vent pipes 33 and 33a. 'Ihe pitch receiver isshut oi intermittently from the vacuum tower and, by means of steampressure through the line 34 from the header 1, the pitch is dischargedfrom the receiver 32 to storage, through valve 15 and pipe 16. When thepitch receiver is being, discharged, the residues are permitted toaccumulate further in the sump 31 of the tower I2, to the extentofsurplus above the amount being recirculated, without deleterious effectupon the color of the distillate. In fact, after the continuousoperation of the distilling apparatus has become stabilized, a pool ofresidue is maintained in the sump` 31 of the tower I2, to the depthpermitted by the height of the inverted syphon loop 24. This pool isheated by the superheated steam issuing .from the nozzle 22 just abovethe pool and is also heated by the metal of the tower bottom, which inturn, derives its heat from the superheated steam. In operation thetemperature of the residue pool is maintained at from 15 to 50 abovethat of the partially finished stock on the bottom tray I3f.

The vapors of pure fatty acids or other distilled material, which arevolatilized from the upper tray, I3a, of the iiashing chamber, by heatfrom the condensation of less pure vapors in the pool of liquid on thattray, and which are mixed with vapors of superheated steam, may be freedof entrained liquid by any wellknown means (such as the baille-plate 40in this instance), and then condensed, also by any means well-known tothose skilled in the arts of distillation; the final residual watervapors,

acids may be 375 to 475 F. (preferably 415 F. for the mixed fatty acidsof tallow greases).

In applying the well-known water spray condensation system at points 43and or 44, 45, it was found that the distillate recovered in thereceiver-separator 46 was small in quantity and contained appreciableamounts of free liquid water as well as some emulsified water. 1overcome these objections entirely by heating the water used in thecondensing sprays nearly to its boiling point at atmospheric pressure.This heated water is conveyed under positive pressure to the'condensingspray-heads and when released through these 'spray-heads into thereduced pressure zone of the vapor pipes 41 and 48, all of the Water iscompletely vaporized, absorbing the heat necessary for its vaporizationfrom the mixed distillate and superheated steam vapors coming from thetower I2. This absorption of heat causes the bulk of the distillatevapors to condense as liquid, entirely free of any liquid water. Thisliquid condensate may be collected in the receiver-separator 46.

Steam at lbs. gauge pressure is taken from the main steam header 1(Figure 1) through the valve 49 and the pipeline 50 to the steam spaceof the preheater 2 where it is utilized to preheat the charging stock ofthe still by means of heat'- exchange. The steam condenses in thepreheater and the condensate water is automatically removed through thepipeline 5I by the steam trap 52, discharging through the pipeline 53into the reservoir 54. The pure condensed water is pumped by the pump 55through the heating coil 56 in the heat exchanger 51 and on through thepipeline 58 to the spray nozzles at 43, 44 and 45. These nozzles may beutilized in any suitable manner, each being controlled by a valve.Steam, water or any suitable fluid may be used as the heating medium forthe pure water passing through the coil 56. In the example shown,

steam at 145 lbs. gauge pressure is taken from exchanger 51 through thepipeline 4c. In the heat exchanger 51, this steam is used to heat thewater passing through the coil 56. This water is heated to 180 to 205 F.and preferably as high as possible without substantial vaporization inthe coil 56 or the pipeline 58. Operation of thev pump 55 is socontrolled that a pressure of from 6 to 12 lbs., normally 8 lbs. gaugeis maintained in the spray water supply pipe 58 at the gauge point 59close to the spray-nozzle locations.

The spray condensing system may be combined with any suitable collectingsystem for recovery of .the condensed distillate. In the example shown(Figure 1), the mixed vapors of steam and distillate entering the outletpipe 4| at 415 to 430 F., are ooled to 325 to 365 normally 350 F.) bymeans of the Hot-Water sprays 43, 44 and 45. Passing through the vaporpipe y 41 into the receiver-separator 46, the bulli of the distillatevapors separates out as liquid fattyv acids in the receiver-separator,from which the liquid condensate flows by gravity through the pipeline60, the -shell-'and-tube cooler 6| and the pipe 62 to the collector 63.In passing through the shell-and-tube cooler 6|, the liquid condensateis cooled to 125 to 175 (normally 135 F.) by means of wateriorvother-cooling iluid and collected in a puremoisture-free state in thecollector 63. From this container it may be pumped continuously by meansof the pump 64 and the pipe 65 to a receiving and storage tank chimneysI5 (a to f) under each bubble cap, overow or downow pipes I6 (a to f),entrainment baille 40, vapor outlet 4|, steam-supply Vnozzle 22 andoveriiow cup-seal 23.

As described hereinbefore, the material to be shallow pool of liquidmaterial of varying com position on each tray in the course of thedescent of said unvaporized portions of the feed stock.

During the distillation operation, superheated steam is supplied 'to thecolumn through the pipe 20, the throttling valve 2| and the nozzle 22.This superheated steam4 on entering the column expands to ll the entirefree space therein below the tray |3f, rises through the vapor chimneysI5f in that tray and bubbles into the shallow pool of liquid on thetray, serving there to heat said pool of liquid and by means of saidheating, also in part by means of the vapor pressure of said steam, tocause vaporization of an appreciable amount of distillable material fromAsaid pool. The mixed vapors of steam and of saidl vaporized distillablematerial then pass upward through the vapor chimneys age of yuncondenseddistillate vapors, pass.

ing uid. Here the remaining distillate vapors arel condensed, the liquidcondensate collecting in the hot-Well receiver 68 and flowing by gravitythrough.V the pipe V69 to the second collector 10, from which thiscondensate is pumped continuously through the pipe 1| by means of thepump 12 to a receiving and storage tank (not shown). The secondcollector 10 is connected to the shell-and-tube Vcondenser 61 by avacuumventv pipe 13 in addition to the.pipe 69. The distillate condensedin the shell-and-tube `condenser and collected in the second collector10 generally contains small quantities of liquid water, but the total ofthis condensate is a very small fraction of the total from'the still,the bulk of the distillate vapors being condensed by the spraycondensing system.

The nalwater vapor, practically free of distillate (vapor or liquid)leaves the shell-andtube condenser 61 by the vapor pipe 14, passing tostandard vacuum apparatus of any suitable l type (not shown).

Referring to Figure 2, which is an'enlarged detail, partly in section,of one form of assembly of a dstilling column with suitable apparatusfor operation of my invention, I2 is any suitable dstilling column intowhich the previously heated material tol be distilled in introducedthrough the pipe 6 and the valve 8. As shown, the column I2 is abubble-tray column |3,f, multiple. bubble caps I4 (a to f), vapor |5e inthe next tray' |3e above, thence through the outlets of the bubble caps|4e into the shallow pool of liquid on the tray I3e. Here substantialportions of the vapors of material vaporized from the lower tray |3f arecondensed, releasing their latent heat of condensation, which serves,with the aid of the superheated steam vapors, to cause volatilization ofdistillable material from the pool on the tray |3e.

This process is repeated on each successive tray in turn as the vaporsrise` through the column. Thus, as the stock to be distilled descendsfrom tray to tray through the overflow pipes I6a to |6f, its content ofdistillable material is progressively reduced.

From the tray |3f the residual stock, which still contains aconsiderable amount of economically distillable material, ows throughthe overow pipe I6f into the cup-seal 23, thence g .into the bottomspace 31 of the distillation column I2.

This bottom space of the column is in free communication -with theresidue receiver 32 through the outlet pipe 3|` and the inverted syphonpipe-loop 24, also through the vent pipes '33 and 33a.

The distillation residues descending into the lower portion of thecolumn I2 ow through the youtlet pipe 3| and rise toward the pipe-loop24 until the ascending portion of the said outlet pipe 3| is lled to alevel 11 corresponding to the level of the intake of the skimming pipe25.

Steam at boiler pressure is takenv from the main steam header 1 throughthe pipe 1, is

the dstilling column. Another portion of the' superheated steam owsthrough the pipe 30 and the valve 29 to the steam-lift pipe 26, inpassing through which it exerts suction on the skimming pipe 25. I

When the pool of distillation residue in the lower portion of the columnI2 reaches the intake level 11 of the skimming pipe 25, the suction ofthe superheated steam passing through the steam-lift pump 26 draws intosaid pump surplus distillation residues above the amount necessary tomaintain in the lower portion of the distillation column I2 a shallowpool with its upper surface substantially level with the intake of theskimming pipe 25. In the steamlift pump 26 the superheated steam mixesdirectly and intimately with the residues withdrawn from the column I2through the skimming pipe 25, and the steam, having been superheated toa temperature higher than that of said withdrawn residues, serves toreheat said residues and at the same time to elevate them through thepipe 21 and to return them to the column I2 through the valve 28, or thevalve 28a, or in part through each of said valves, as desired.

The residues thus returned to the distilling column then mix, on thetray I4d or the tray I4e, or in part on each of these trays, with theundistilled material descending through the column. In this manner thesaid residues are reheated by the superheated steam in the steamliftpump and are subjected to further distillation eiect when returned tothe column, additional quantities of vaporizable material being thusremoved from the residues.

When the mixture of superheated steam and reheated distillation residuesenters the distilling column I2 through the valve or valves 28 and 28a,the superheated steam expands and rises through the vapor chimneys I5 (dto a) and bubble caps I4 (d to a) of the upper trays I3 (d to a) andimparts to the pools of liquid on those trays additional heat and vaporpressure, thus contributing to distillation of vaporizable material fromsaid pools and to the maintenance of .distillation temperatures therein.

The volume of distillation residues descending from the tray I3f throughthe pipe I6f and the cup-seal 23 into the lower portion or sump 31 ofthe distilling column I2 may be continuo sly increased by increasing theamount of supe 'heated "steam admitted to the steam-lift .pump 26(thereby increasing the volume of residues recycled to the distillingcolumn).

`As the volume of distillation residues descending from the tray I3finto the lower portion of the distilling column increases it tends toexceed the amount recirculated and the pool 18 of liquid residues in thelower portion of the column gradually increases in depth until itreaches the level 19 corresponding to the overflow point of the ventedpipe-loop 24. When this condition is reached the contents of the'residue'pool 18 start to discharge gradually through the pipe 3l and the loop24 into the residue receiver 32. Because of the withdrawal of quantitiesof residue by the steam-lift pump 26 through the skimming pipe 25, onlythe heaviest portions of said residue, that is, those portionscontaining a low proportion of distillable material, sink into thatportion of the pool 18 which is below the level 11 and these heaviestportions of the residue flow thence through the pipe 3| andthe ventedpipe-loop 24 to the residue receiver 32. In addition, under theconditions of 'high temperature and low absolute pressure existing in tothe residue receiver 32 through the pipe 3| and the vented pipe-loop 24.

The residue receiver 32 is discharged intermittently through the valve15 and the pipe 16, by admission to the receiver of steam pressurethrough the pipe 34, valves on the lines 24 and 33 being closed at suchtimes. During such intermittent discharge of the contents of thereceiver 32 the residue pool 18 may increase slight- 1y in volume, butrecycling and reheating of residues by means of Asuperheated steam inthe steam-lift pump.26 is 4not interrupted and when the valves on lines24 and 33 are re-opened, the level of the residue pool isautomatically-readjusted to the height 19. v

Substantially in the manner hereinabove described the residues in acolumn distillation are recycled with economical reheating of suchrecycled residues; promoting increased efficiency of separation ofresidues and additional recovery of distilled products from saidresidues; and as a corollary of said reheating, economically supplyingadditional heat to the intermediate and upper portions of the distillingcolumn, while simultaneously performing a continuous selectiveseparation of distillation residues, reheating and recycling to thedistilling column a portion of the residue containing economicallyrecoverable distillable material, while discharging away from thedistilling column another portion of the residue from which suchdistillable material has been recovered.

As an example of operation under the process hereinbefore described, thefollowing distillation has been carried out. The distilling bubble traycolumn utilized was approximately 15 feet high and 6 6"- in internaldiameter at the top (crosssectional area 33.2 square feet). The towercontained six bubble trays' spaced 22" apart, the bottom tray being 30"above the bottom of the tower. The upper tray contained 84 bubble caps,each cap being 5" in external diameter. The total eiective distillingarea of the upper plate was therefore 21.75 square feet. The top vaporoutlet of the tower was 16" internal diameter. Below the vapor outlet aconical-shaped baille plate 4l" in greatest diameter was inserted. Theannular space through which all vapors passed between this baffle plateand the upper portion of the tower wall was 28.25 square feet in area.

Steam was admitted to the tower through a 3" pipe below the bottom tray,but above the maximum height of the pool of residue on the bottom of thetower. The material to be distilled, after atomization by steam, wasadmitted to the heater through two two-inch tubes in parallel andy afterleaving the heating zone the two portions were combined in onethree-inch pipe through which the mist of atomized fatty acids and steamentered the distilling tower in its upper portion. Pressure slightly inexcess of atmospheric was `maintained in the tubes of the heater.

During a continuous run of 911/2 hours, 180, 900 pounds of Twitchellizedbrown grease fatty acids containing 96.2% of free fatty acids(calculated A lof 95.8%.

ards of the American Society for Testing Mateas oleic acid), were fed tothe still, or at an average rate of 1977 pounds per hour. 173,390 poundsof distillatewere recovered, having color of between 1 and 11/2 A. S. T.M., representing a yield (A. S. T. M. refers to the color standrials,which are well-known to those skilled in the art of distillation.) A

During this period 3202 lbs. of steam were fed to the charge through theatomizing device, an average of 35 lbs. per hour.

There was added also a total of 86,790 lbs. of

superheated steam (an average of 948.5 lbs. per' per 1977 lbs. ofcharge, or approximately 29 parts of steam by volume toeach part offatty acid charge.

This atomized mixture of fatty acids and steam entered the mist heatertubes 5, 5 at a temperalture of 227 F. and was heated therein to 495 to530 F. with a. normal temperature of 510 F. Passing then to thedistilling column through the line 6 and the valve 8, the atomizedmixture entered the column above the tray |30 and was cooled byexpansion and evaporation so that the temperature .of the liquid poolformed on the tray i3c was 425 to 440 F., normally 430 F.

A lai ge portion of the fatty acids was vaporized at once and passedupward as vapor throughthe distilling column. The unvaporized portionlformed a pool on the tray l3c and overowed therefrom to the lower traysinsuccession. As the unvaporized residue of the stock descended throughthe tower, successive additionalportions of the fatty acids werevaporized from each tray and the temperature of the residue graduallyrose until on the bottom tray l3f). the temperature was525 F. to 550 F.,with normal temperature of 525 F. From this trayA the remainingunvaporized residue overflowed into the up 23 and thence to the bottomofthe tower. When the pool of residue so formed in the sump 3l of thetower reached the height of the intake of pipe 25,l 4 inches above thebottom of the tower, the lift-pump 26 commenced drawing the residuethrough the pipe 25, mixing it with superheated steam to reheat it anddischarging it above the plate I3d where it joined the stream ofunvaporized stock descending through the distilling column. When thetotal of unvaporized stock descending in the tower became greater thanthe amount returned by the lift-pump to plate i3d, a pool was formed inthe bottom of the tower. The depth of this pool was controlled (by theoutlet pipe loop 24) at 13 inches above the bottom of the tower. Whenthe pool started'to exceed this depth, all surplus unvaporized residueflowed from the bottom of the pool through the pipe loop 24 into thepitch receiver 32, whence it was discharged intermittently to a storagetank (not shown) by means of steam pressure adture on the bottom traybecame 580 to 610 F., normally 595 F. and the temperature of the pool ofresidue in the bottom of the tower became 616 to 635 F., normally 615 F.

The vapors rising inthe distilling column had an exit temperature ofl410 to 430 F., normally 420 F. and were cooled immediately upon leavingthe tower, so that the residual vapors leaving the receiver-separator 46had atemperature of 340 to 367 F., normally 350 F. In the shelland-tubecondenser 61, the vapors were further cooled to an exit temperature of115 to 140, normally" 125 F., and here substantially the entireremainder of the uncondensed fatty acid vapors was condensed, collectingin the hot-well 68y and flowing to the second collector 10. The lcondensed fatty acids owing from the receiverseparator 46 were cooled inthe shell-and-tube cooler 6| to 125 to 160 F., normally 135 F. Thiscondensate was free of water. The condensates from both collectors werepumped to 'a single storage tank, where they were combined i inanticipation of further processing or shipment.

vDuring the period of operation 3,365 gallons of condensed water (anaverage of 36.8 gallons per hour) were pumped from the reservoir 5l bythe pump 55 through the heat exchange coil 56, the line 58, land thethrottle or pressurerelief valves to the spray-nozzles 43, 44 and 45.The temperature of thev water used in the sprays was 198 to 200 F.,normally 200 F. The pressure of this water i'n the supply pipe 58 nearthe lspray-outlets was 3 to 8 lbs. per square inch,

normally 6 lbs. per square inch, above atmospheric pressure.

TheI plant steam pressure utili'zed was 148 lbs. per square inch gaugewith total temperature of 365 F. The superheated steam had pressure of6.5' lbs.' gauge and temperature of 850 F. be fore entering the bottomof the tower and the lift-pump. variations of pressure being observedbetween 5 lbs. and 7 lbs. gauge and temperature range from 830 to 880 F.The pressure o! steam before entering the atomizing mixer was 18 lbs.gauge, temperature 255 F.

Absolute pressures maintained in the system were as follows:v

Inches of mercury My new process may be used likewise in otherdistillations where it is desired to obtain maximum recovery ofdistillable material and to reduce the distillation residues to aminimum content of distillable substances. It may be used also for thedeodorization and/or purification of fatty oils or mineral oils or otherorganic liquids containing volatile components. The fatty acidsmentioned in the foregoing can be substituted, for instance, bypetroleum oils, particuthetemperature of the recycling stock and of thedescending stock in the lower portion of the column was gradually raiseduntil the temperalarly by lubricant stocks or by asphalt-base crudeoils, or by waxes, by tars or by 'asphalts,.

The foregoing detailed description has been given only for clarity ofunderstanding and no unnecessary limitations should be understoodtherefrom, but theappended claims should be construed as broadly aspermissible, in view of the prior art.

What I claim is:

1. In a process for steam distillation of organic liquids yielding tarryor fluid residuums in a tube and chamber distilling apparatuscharacterized by maintenance of a succession of pools of liquid ofcomposition varying from top to bottom of the distillingi chamber, thesteps which comprise maintaining in a lower zone of the distillingchamber a liquid body-of controlled substantially uniformdepthconsisting of a mixture of distillation residuum and distillable liquid,continuously withdrawing residuum having minimal content of distillableliquid from a lower zone of said liquid body, continuously withdrawingresiduum having substantial content of distillable liquid from an upperzone of said liquid body while maintaining said liquid body atsubstantially uniform depth, reheating said continuously withdrawnresiduum having substantial content of distillable liquid by means ofdirect admixture 'with superheated steam of higher temperature than saidwithdrawn residuum in a steam-lift device communicating through itsdischarge outlet with a higher zone of said distillating chamber at a.

point below the point of liquid feed to said chamber having one or moreliquid pools of said chamber intervening below said discharge outletcommunication and above said liquid body of controlled substantiallyuniform depth and discharging the resultant mixture of superheated steamand reheated residuum having substantial content of distillable liquidinto said higher zone of said distilling chamber.

2. In a process for steam distillation of material containing fattyacids yielding tarry or fluid residuums in a tube and chamber distillingapparatus characterized by maintenance of a succession of pools ofliquid of composition varying from top to bottom of the distillingchamber, the steps which comprise maintaining in a lower zone of thedistilling chamber a liquid body of controlled substantially uniformdepth consisting of a mixture of distillation residuum and distillablefatty acids, continuously withdrawing residuum having minimal content ofdistillable fattyacids from a lower zone of said liquid body,continuously withdrawing residuum having substantial content ofdistillable fatty acids from an upper zone of said liquid body whilemaintaining said I munication and above said liquid body of controlledsubstantially uniform depth and discharging the resultant mixture ofsuperheated steam and reheated residuum having substantial content ofdistillable fatty acids into said higher zone of said distillingchamber.

3. In a process for steam distillation of organic liquids yielding tarryor uid residuums in a acterized by maintenance of a succession of poolsof liquid of composition varying from top to bottom of the distillingchamber, the steps which comprise continuously withdrawing residuumhaving substantial content of distillable liquid from a lower zone ofthe distilling chamber, reheating said continuously withdrawn residuumby means of direct admixture with superheated steam of highertemperature than that of said withdrawn residuum and discharging theresultant mixture of superheated steam, residuum and `tube and chamberdistilling apparatus chardistillable liquid into a higher Izone of saiddistilling chamber at a point below the point of liquid feed to saidchamber having one or more pools of liquid intervening below the pointof said discharge and above the lower zone of residuum withdrawal ofsaid distilling chamber.

4. In a process for steam distillation of material containing fattyacids yielding tarry or fluid residuums in a tube and chamber distillingapparatus characterized by maintenance of a succession of pools ofliquid of composition varying from top to bottom of the distillingchamber, the steps which comprise continuously withdrawing residuumhaving substantial content of distillable fatty acids from a lower zoneof the distilling chamber, reheating said continuously withdrawnresiduum by means of direct admixture with superheated steam of highertemperature than that of said withdrawn residuum and discharging theresultant mixture of superheated steam, residuum and distillable fattyacids into a higher zone of said distilling chamber at a point below thepoint of liquid feed to said chamber having one or more pools of liquidintervening below the point of said discharge and above the lower zoneof residuum withdrawal of said distilling chamber. 5. The process ofsteam distillation of organic liquids yielding tarry or iluid residuumswhich comprises passing the distillation feed stock through a restrictedpassage in a heating zone, further passing said feed stock after heatinginto a distilling zone characterized by maintenance ofy a succession ofpools of liquid of composition varying from top to bottom of saiddistilling zone, maintaining in a lower portion of said distilling zonea liquid body of controlled substantially uniform depth consisting of amixture of distillation residuum and distillable liquid, continuouslywithdrawing residuum having minimal content of distillable liquid from alower zone ofl said liquid body, continuously withdrawing residuumhaving substantial content of distillable liquid from an upper zone ofsaid liquid body while maintaining said liquid body at substantiallyuniform depth, reheating said continuously withdrawn residuum havingsubstantial content of distillable liquid by'direct admixture withsuperheated steam of higher temperature than said withdrawn residuum ina steam-lift device communicating through its discharge outlet with a.higher portion of said distilling zone at a point below the point ofliquid feed to said distilling zone having one or more liquid pools ofsaid distilling zone intervening below said discharge outletcommunication and above said liquid body of controlled substantiallyuniform depth, discharging the resultant mixture of superheated steamand reheated residuum having substantial content of distillable liquidinto said higher portion of said distilling zone, passing all thevapors-of distillation into a condensing zone and condensing andremoving the distillate.

6. The process for steam distillation of organic having substantialcontent of distillable fatty liquids yielding tarry or uid residuumswhich comprises passing the distillation feed stock steam, residuum anddistillable liquid into a higher portion of said distilling zone at apoint below the point of liquid feed to said distilling zone having oneor more pools of liquid intervening below the point qf said dischargeand above the A point of residuum withdrawal of said distilling zone,passing the vapors of distillation into a condensing zone and condensingand removing the distillate.

7. The process of stem distillation of material containing fatty acidsyielding tarry or fluid residuums which comprises passing thedistillation Afeed stock through a restricted passage in a heating zone,further passing said feed stock after heating into a distilling zonecharacterized by maintenance of a succession of pools of liquid ofcomposition varying from top to bottom of said distilling zone,maintaining 'in a lower portion of said distilling zone a liquid body ofcontrolled substantially uniform depth consisting of a mixture ofdistillation residuum and distillable fatty acids, continuouslywithdrawing residuum having minimal content of distillable fatty acidsfrom a lower zone of said `liquid body, continuously withdrawingresiduum having substantial content of distillable fatty acids from anupper zone of said liquid body while maintaining said liquid body atsubstantially uniform depth, reheating said continuously withdrawnresiduum acids by direct admixture with superheated steam of highertemperature than said withdrawn residuum in a steam-lift devicecommunicating through its vdischarge outlet with a higher portion or'said distilling zone at a pointv below the point of liquid feed to saiddistilling zone having one or more liquid pools of said distilling zonein- -tervening below said discharge outlet communication and above saidliquid body of controlled substantially uniform depth, discharging theresultant' mixture of superheated steam and re-` heated residuum havingsubstantial content of distillable fatty acids into said higher portionof said dtilling zone, passing all the vapors of distillation into acondensing zone and condensing and removing the distilled fatty acids.

8. The process for steam distillation of material containing fatty acidsyielding tarry Aor uid residuums which comprises passing thedistillation feed stock through a restricted passage in a heating zone,further passing said feed stock after heating into a distilling zonecharacterized by maintenance of a succession of pools of liquid ofcomposition varying from top to bottom of said distilling zone,continuously withdrawing residuum having substantial content ofdistillable fatty acids from a lower portion of said distilling zone,reheating said continuously withdrawn residuum having substantialcontent of distillable fatty acids by direct admixture with superheatedsteam of higher temperature than that of said withdrawn residuum,discharging the resultant mixture'of superheated steam, residuum anddistillable fatty acids into a higher portion of said distilling zone ata point below the point of liquid feed to said distilling zone havingone or more pools of liquid intervening below the point of saiddischarge and above the point of residuum withdrawal of said distillingzone, passing the ALAN PORTER LEE.

